In the prior art, hot air may be stored in a transparent covering such as a greenhouse. Specifically, sunlight emits into and heats the air inside the greenhouse, the inside air could not mingle with the outside air by the greenhouse, the temperature inside the greenhouse is higher than the temperature outside the greenhouse, and thermal energy is accumulated in the greenhouse. However, greenhouse is mainly constructed of members such as boards or beams for withstanding bending moment and walls or columns for withstanding the weights of the components, such a construction will have a larger sectional area and weight, and the sectional area increases along an increase in dimensions such as length, width, height, etc, as a result, it is difficult to produce this type of structure with a very large area and volume.
In the prior art, a large volume of air may be stored in a structure body such as a conventional pneumatic structure with a skin formed by air tight films and equipments such as blowers for providing pressure difference between two sides of the skin. Its pressure difference distribution is different from that caused by the buoyancy of hot air. In the latter case, the pressure difference between the inside and outside of the covering which is filled with hot air is about zero at the two sides near the air inlet and increases progressively from bottom to top of the covering. In the former case, the pressure difference between the inside and outside of the pneumatic structure does not vary with height. Therefore, the actions of structural mechanics on the two structure bodies are quite different. In the latter case, the pressure difference between the inside and outside on the lower portion of the skin is relatively small and a gap communicating the inside and outside of the skin may exist at the lowest portion of the skin. In the former case, however, the pressure difference between the inside and the outside does not vary with height and the adjoining line between the skin and the field is tight. In addition, the buoyant forces of the conventional pneumatic structures are mostly accumulated into heavy force on the surrounding edge part of the skin. Therefore, the stress borne by each component increases as the size of the structure increases; as a result, the range of structure and the volume formed thereof are limited by these factors and difficult to be large.
Conventionally, artificial rain technique uses aircraft or rocket to disseminate silver iodide or dry ice capable of producing ice forming nuclei into clouds to increase rainfall, or burns silver iodide on the ground and discharges the smoke with silver iodide particles into the updraft of a front when the front comes. In general, the aforementioned artificial rain technique can make the super-cooled water droplets of below −5° C. quickly freezing into ice crystals and releasing latent heat and thereby developing clouds and achieving an effect of increasing approximately 10% of rainfall. However, the conventional artificial rain technique needs synchronization of weather conditions; that is, the conventional artificial rain technique may not achieve the expected effect if there is no heavy cloud or front etc. coming. For example, cloud or front may not appear at the area suffering long-term drought; therefore, the conventional artificial rain technique may not be effective for relieving drought due to that the conventional artificial rain technique cannot actively promote the occurrence of heavy clouds and fronts. In addition, target of the conventional artificial rain technique is mesoscale cloud (having a horizontal width about ten kilometers to hundreds of kilometers); that is, the conventional artificial rain technique is adapted for a large area.
Another conventional artificial rain technique is that: based on meteorology document, a large area of forest fire or a violent house fire may lead to local rainfall due to that fire may release a huge amount of thermal energy to the lower atmosphere, and thereby increasing the atmospheric instability in the local region. Therefore, convective cells lifting from lower atmosphere may develop into cumulonimbus and rainfall when violent fire and slightly more unstable weather condition occur simultaneously. Weather experts had attempted to adopt the means of the large scale of burning on the ground to increase thermal energy in the lower atmosphere thereby promoting rainfall; however, a large scale of burning is not only uneconomical but would also cause environmental pollution and disasters. Therefore, the conventional artificial rain technique is no longer developed and executed.